DESCRIPTION

Suppose you have a class (like Food::Fish::Fishstick) that is derived,
via its @ISA, from one or more superclasses (as Food::Fish::Fishstick
is from Food::Fish, Life::Fungus, and Chemicals), and some of those
superclasses may themselves each be derived, via its @ISA, from one or
more superclasses (as above).

When, then, you call a method in that class ($fishstick->calories),
Perl first searches there for that method, but if it's not there, it
goes searching in its superclasses, and so on, in a depth-first (or
maybe "height-first" is the word) search. In the above example, it'd
first look in Food::Fish, then Food, then Matter, then Life::Fungus,
then Life, then Chemicals.

This library, Class::ISA, provides functions that return that list --
the list (in order) of names of classes Perl would search to find a
method, with no duplicates.

FUNCTIONS

the function Class::ISA::super_path($CLASS)

This returns the ordered list of names of classes that Perl would
search thru in order to find a method, with no duplicates in the list.
$CLASS is not included in the list. UNIVERSAL is not included -- if
you need to consider it, add it to the end.

the function Class::ISA::self_and_super_path($CLASS)

Just like super_path
, except that $CLASS is included as the first
element.

the function Class::ISA::self_and_super_versions($CLASS)

This returns a hash whose keys are $CLASS and its
(super-)superclasses, and whose values are the contents of each
class's $VERSION (or undef, for classes with no $VERSION).

The code for self_and_super_versions is meant to serve as an example
for precisely the kind of tasks I anticipate that self_and_super_path
and super_path will be used for. You are strongly advised to read the
source for self_and_super_versions, and the comments there.

CAUTIONARY NOTES

* Class::ISA doesn't export anything. You have to address the
functions with a "Class::ISA::" on the front.

* Contrary to its name, Class::ISA isn't a class; it's just a package.
Strange, isn't it?

* Say you have a loop in the ISA tree of the class you're calling one
of the Class::ISA functions on: say that Food inherits from Matter,
but Matter inherits from Food (for sake of argument). If Perl, while
searching for a method, actually discovers this cyclicity, it will
throw a fatal error. The functions in Class::ISA effectively ignore
this cyclicity; the Class::ISA algorithm is "never go down the same
path twice", and cyclicities are just a special case of that.

* The Class::ISA functions just look at @ISAs. But theoretically, I
suppose, AUTOLOADs could bypass Perl's ISA-based search mechanism and
do whatever they please. That would be bad behavior, tho; and I try
not to think about that.

* If Perl can't find a method anywhere in the ISA tree, it then looks
in the magical class UNIVERSAL. This is rarely relevant to the tasks
that I expect Class::ISA functions to be put to, but if it matters to
you, then instead of this:

@supers = Class::Tree::super_path($class);

do this:

@supers = (Class::Tree::super_path($class),'UNIVERSAL');

And don't say no-one ever told ya!

* When you call them, the Class::ISA functions look at @ISAs anew --
that is, there is no memoization, and so if ISAs change during
runtime, you get the current ISA tree's path, not anything memoized.
However, changing ISAs at runtime is probably a sign that you're out
of your mind!

COPYRIGHT

Copyright (c) 1999, 2000 Sean M. Burke. All rights reserved.

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.